* Add DEBUG flag to build PRX, don't build by default (shrinks binary by 700kB)
* Add some MAKEFLAGS to enable multiple processes (multithread building)
* Renamed Application to "Nazi Zombies: Portable"
* Lowered firmware version requirement to 4.00
* Clear unneeded library links
* have `make clean` remove the build directory instead of leaving it
Introduces a lot of changes to induce POSIX compliancy, and fix weird
compilation quirks that the old GCC ignored. Also removes some old
Makefiles that were just lying around. :^)